The growth of animal cells is controlled by external factors at a few hours prior to DNA synthesis. Cancer cells are deranged in this control. The proposed work is designed to continue our studies on the biochemical events that occur during this control period, and their derangements in cancer cells. Studies on cell cycle progression led to our proposal that a key component is a rather short-lived protein (in normal cells) that is stabilized in various cancer forming cells. Such a protein was identified using 2D gels. Antibody will be prepared against this protein, to facilitate its further study in the cell (location, timing of synthesis) and in extracts (properties, basis for changed stability in cancer cells). Microinjection of the protein into mammalian cells or Xenopus oocytes will be done to study its function in turning on DNA synthesis. The initiation of DNA synthesis involves production of enzymes of the DNA pathway, and their assembly in the nucleus, into a multienzyme complex. These enzymes, and also the corresponding mRNAs, will be studied as to control of their formation through cloned probes. Somatomedin C appears to be required for the final steps. Roles of somatomedin C and of the labile protein in production of the enzymes and of the multienzyme complex will be studied. A longer term goal will be to clone the gene for the labile protein, from cancer and normal cells to investigate its function and sequence, and to see whether it has oncogene activity, by transfection.